Resistor and spabk plug embodying



Jan- 18, 1949 T. G. McDouGAL Erm. 2,459,282

RESISTOR AND SPARK PLUG EMBODYING SAME Filed lay 24, 1943 Patented Jan. 18, 1949 RESISTOR AND SPARK PLUG EMBODYING SAltIE Taine G. McDougal, Flint, Karl Schwartzwalder, Holly, and Alexander S. Rulka, Flint, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application May 24, 1943, .Serial No. 488,114

22 Claims.

This invention has to do with resistors particularly suitable for use in wiring harness and in spark plugs. Such `resistors are commonly used to suppress the high frequency oscillations associated with spark discharge in ignition systems. Such oscillations sometimes cause rupture of the ignition cable and always cause increased erosion of the electrodes.

Heretofore separate resistors have been used for this purpose. Difliculty has been encountered with them because of the tendency of the spark to ash over the outside of the resistance element, particularly at high altitudes, as well as because of large variations in resistance with the changes in temperature encountered during operation of the engine. We have overcome both of these difficulties with the constructions herein disclosed.

According to our invention the resistor comprises a sleeve of insulating material within which is secured the resistance element. The resistance element is sealed within the sleeve so as to exclude air and moisture which might adversely affect it.

The parts referred to are preferably made either Wholly or partly of ceramic material so that they may be bonded or fused together by subsequent ring. The bonding of the resistance element to the sleeve makes it impossible for the current to flash over the outside of the resistor. The resistance element is preferably confined well within the sleeve so as to increase the length of the path by which flash-over might take place around the exposed surface of the sleeve, thereby rendering hash-over less likely.

The resistance element is preferably sealed within the sleeve by conducting material having A a ceramic base so that it may be bonded to the resistance element as well as to the sleeve on the same firing.

In one form of the invention the sleeve is conshell provided with side electrodes I2 and having an insulator I4 suitably secured therein. In this form of the invention the insulator constitutes the sleeve previously referred to. The insulator is preferably of the sintered oxide type consist ing either wholly of aluminum oxide or of a preponderance of aluminum oxide, together with other oxides, such as magnesium oxide, beryllium oxide or suitable silicates such as mullite. If preferred, the insulator may be a porcelain body characterized by a preponderance of mullite, Zircon, zirconia or the like, together with glass.

The insulator is provided with the usual central aperture I6 to receive the electrode. The electrode comprises a lower section I8 which may be of any suitable material capable of withstanding high temperatures and possessing goed heat conductivity, preferably nickel alloy filled with copper as described in Heller Patent 2,296,033. Section I8 is provided with a shoulder 2li resting on a shoulder provided in the bore in the insulator. 2,2 indicates generally the ceramic section of the electrode and 24 the upper section which is preferably of metal such as steel.

The ceramic section of the electrode comprises a lower seal 26, an upper seal 28, and an intermediate portion 30 constituting the resistance element.

The conducting seals may be made of any suitable material capable of being bonded to the insulator and to the resistance element and possessing relatively good electrical conductivity. We prefer to employ a mixture of glass and conducting material as described and claimed in Schwartzwalder and Kirk Patent No. 2,106,578 granted January 25, 1938, and in Schwartzwalder and Rulka Patent No. 2,248,415 granted July 8, 1941.

The lower seal 26 which is subjected to greater heating during operation of the plug is preferably made from a mixture consisting of 55 parts powdered copper, 45 parts Pyrex or borosilicate glass, together with 3 parts of a suitable binder such as Dritex, a hydrogenated cotton-seed oil.

The upper seal, which is less exposed to heat, is preferably made up of a lower portion 28' of the composition just described and an upper portion 28 consisting of a similar mixture of copper, glass and binder, except that the glass employed possesses greater plasticity, preferably consisting of a lead borosilicate composition as described in said Schwartzwalder and Rulka patent.

A great deal of work has been done with different compositions of material for the resistance element in an effort to nnd one having the least possible variation in resistance over the temperature range encountered during the use of the plug. We have had the most success with a resistor of the following composition:

- y Percent Borosilicat'e glass (Pyrex culletl 62.4 Fluorspar ('CaFz) 25.2 l Magnesium borate glass 7. 8 Thermae carbon 4.6l

These materials are mixed together to gire a uniform mixture. Water is added in proportion of 40 parts of water to 100 parts of materialiby weight. The wet mass is then dried to remove enough Water to permit granulatioh of the`niate-- rial through a 20 mesh screen and their cor'n-' pletely dried, This thoroughlyY dried material. is then re-screened to pass a 20 mesh screen and is ready for use.

The composition above: given is susceptible of considerable modification; The resistance may be reducedr by increasing the amount of carboni and maybe increased' by decreasing the amountof carbon.

We'have used'variou's'forms of carbon black butV have had' best results' with' carbon. black known' as Thermax employing. the coarsest particle size; obtainable, this being on the order of 1.12`l microns as' determined by the' ultra-microscopic method. ThermaX is` a carbonv black produced in an oxygen free atmosphere by thermal decomposition of natural gas.

Pyrex or borosilicate glass possesses a low coeiicient of expansion as' Well as ability to resist heat. The magnesium' berate' glassI likewise possesses' al. low coeiiicient of expansionand appears to give an? elastic quality to the resulting glass which reduces' strain-s Fluorspar is; added to'increase the thermalgexpansionl of the resulting seal.

Resistances of the above cornpositionz have been` made having values onl the order of from 60v to 100 ohms; If' higher resistances or"substantiallyl the same size are desired it may be found desirable to'V modify the compositions as indicated below:

Rcfsitancc Restzncc Rs'stnce o ner of rc1' o rer Composmm or 500 of 5,000 of 10,000

Ohms Olins Olinis GroundPyr'ex collet. 638` 6315 0410 Magnesium berate glass 8. 0 9. 0 9. 0 Fluorspar 25. G 11. 0 11, 0' Vhiting 15.0 Beryl 15.0 Thermax carbo 7 G 1.5 1.0

Percent Pyrex` glass 27.5 Glass,y preferably consisting of 95% B203 and 5% MgO..v 25 Boron carbide 37.5 Tungsten carbide together with 3.0% of a suitable binder such as Dritex 10.0

Boron carbide and tungsten carbide' act as conducting materials and' when usedY together seem to have the effect of reducing variation of resistance with passage of time. Boron metal may be used in place of tungsten carbide if desired. Other heat resisting conducting materials may be used With the glass or other ceramic materialto make the resistor, for example, variousrnetallicI carbides or oxides with or without the additions of metals. Carbon may be incorporated in the glass either alone or in combination with the other resistance materials mentioned; The" carbon used is preferably in the form of carbon black.

In the manufacture of the spark plug the insulator is made in the usual manner. The temperatures required in tiring the insulator will be Within the range of from approximately 1450" to 1'7-50" C. depending upon the composition employed.

In: assembling the center electrode in the insulator, the lower section I8 is dropped in place, a measured amount of copper-glass seal in powdered' form is fed into the bore and tamped in place. Any loose powder is blown out of the insulator to'prevent contamination of the resistor.

iThe desired amount of powdered resistance material isthen placed in the bore and tamped, followed by a measured portion of powdered copper glass seal and more tainping; and then by a small quantity of the powdered mixture of copper and lead-borosilicate glass. The upper electrode section 241s then inserted in the bore and the Whole assembly is heated to approximately 1600" Fl When the glass is sufficiently softened pressure isy applied to the upper electrode section to? force it down into the bore, thereby compressing the softened material and causing the more iluid copper lead-borosilicate sealing material to surround and grip the part 2G.

In Figure 2v the invention' is shown embodied in a resistor 35` adapted for use in a wiring system,

for example in the high tension leads of the ignition system of an aircraft engine.

The resistor 35 is illustrated as enclosed in a metal sleeve 42 provided with cooling iins as shown. The sleeve 2 has threaded engagement at one end with cape-l secured by bolts iii to the distributor housing cover 48'.

'Ifhe resistorv consists of a sleeve 34 of either sintered oxide or porcelain composition, the same as the insula'tor'-v I4 of Figure 1. However, if desired, some other suitable insulator composition may be employed asthe sleeve IM is not subjected to the same thermal and electrical stress as a spark plug" insulator. Within the sleeve and integrally bonded thereto is a resistance element 36 preferably ofthe same composition as the resistance element 30 of Figure 1. The resistance elene'nt is sealed within the sleeve 34 by glass seals 38 which may be of the same composition as the seals disclosed in Figure 1, the outer portion of they glass seals, if desired, being formed of a more fusible glass such as indicated at 23" in Figure 1-. The glass seals secure within the sleeve 34' metal terminals Eil, one of which is in electrical Contact with cable E2 coming from the ignition coil While the other is in conducting relation With cable 5@ leading to the distributor. Suitable means, not shown, will be provided to hold the cables in the position indicated. The glass seals form a good bond with the terminals 5B and452 just as they do With the metallic sectionsl of the electrode illustrated in Figure 1.

The method 0I manufacture of this resistor is substantif he saine that of the plug. One

" o` th'e'teimmels Eli is inserted in the sleeve, the

glass seal material in powdered form is inserted, followed by the powdered resistance material and the powdered ingredients of the second seal. The other terminal is then inserted and the assembly is heated to soften the glass, thereupon pressure is applied to the terminals to cause them to seat in the glass as shown. In this operation suitable stops are provided to insure the centering of the resistance element in the sleeve.

It may be found desirable to provide the resistor of Figure 2 with a silver coating on the out side as illustrated at 40 to permit better heat transfer to the metal housing in which the re-v sistor and the ignition cable are usually mounted, the housing shielding the cable and preventing interference with radio communication. Obviously the resistor can be used wherever it is desired to employ a fixed resistance unaffected throughout a considerable range of temperature.

The described construction has many advantages. Owing to the integral assembly of resistor and insulator or shell, there is no possibility of the high tension current flashing over the sides of the resistor as sometimes happens when independent resistors are employed at high altitudes. The resistance element is sealed from attack by gases and vapors by the conducting seals. The resistance elements provide a constant resistance over a Wide temperature range. This range is the greatest in the case of the preferred composition containing carbon black.

The resistance may be varied by increasing the proportion of glass or other ceramic base material. It is also possible to decrease the resistance by increasing the pressure employed in the assembly operation or by increasing the temperature during assembly thereby producing betn ter contact between the particles making up the seal.

While glass is preferred as the ceramic base for the resistance element and conducting seals, especially vborosilicate glass because of its low expansion and resistance to heat, as well as its vrelative low softening temperature, it may in some instances be found desirable to employ material having greater heat resistance such as sintered oxides or mixtures of sintered oxides and silicates. The ceramic material employed should not soften within the range of temperature to which the resistor is subjected in use, for it has been found if that is the case the resistance increases with time.

The preferred form of resistance material expands less upon heating than does the usual alumina base insulator, so that when contraction takes place after the assembly operation the insulator or shell tends to grip the resistance element and seals insuring tightness.

This is a continuation in part of application Serial No. 407,844, led August 22, 1931 by the same inventors.

We claim:

l. The combination of a sleeve of ceramic insulating material, a resistance within and closing the passage through the sleeve and comprising a mixture of glass and carbon black fused in place and thermally bonded to the sleeve, and a seal comprising a mixture of` glass and conducting material overlying one end of the resistance element fused in place and thermally bonded to the resistance and to the sleeve and protecting the element from the atmosphere.

2. The combination of a sleeve of ceramic insulating material, a resistance within and closing the passage through the sleeve and comprising a mixture of glass and carbon black fused in place and thermally bonded to the sleeve, and. seals comprising a mixture of glass and conducting material overlying the ends of the resistance element and fused in place and thermally bonded to the resistance and to the sleeve and protecting the element from the atmosphere.

3. A resistor comprising a sleeve of insulating material, a resistance element within and closing the passage through the sleeve and thermally bonded thereto, and seals overlying the ends of the resistance element and thermally bonded thereto and to the sleeve, the ends of said sleeve overhanging the ends of said resistance element thereby providing a long leakage path to prevent flash-over.

4. A resistor comprising a sleeve of insulating material, a resistance element within and closing the passage through the sleeve and thermally bonded thereto, and seals overlying the ends of the resistance element and thermally bonded thereto and to the sleeve, the ends of said Sleeve overhanging the ends of said resistance element, said sleeve having an exterior coating of conducting material.

5. A spark plug comprising a shell, an insulator in the shell having a bore therein and an electrode section in the bore, a seal having good electrical conductance securing and sealing said section in the bore and rendering said bore impervious to gases, and a resistance element in the bore in series with the section and seal and bonded to the insulator and to the seal, the resistance of said element being sufiicient to substantially reduce erosion of the electrode by spark discharge.

6. A spark plug comprising a shell, an insulator in the shell having a bore therein and an electrode section in the bore, a seal having good electrical conductance securing and sealing said section in the bore and rendering said bore impervious to gases, and a resistance element in the bore in' series with the section and seal and bonded to the insulator and to the seal, the resistance of said element being sufficient to substantially re' duce erosion of the electrode by spark discharge, and a second conducting seal bonded to the other end of the resistance element and to the insulator, said conducting seals protecting said resistance element, while the bonding of the resistance element to the insulator prevents flash-over.

7. A spark plug comprising a shell, a ceramic insulator in the shell having a bore therein, an electrode section in the bore, a ceramic base seal having good electrical conductance overlying one end of said section and securing and sealing said section in the bore, said seal being bonded to the insulator and rendering said bore impervious to gases, and a ceramic base resistance element in the bore bonded to the insulator and to the seal Vand constituting a part of the electrode in series having good electrical conductance overlying oneend of said section and securing and sealing said section in the bore, said seal being bonded to the insulator and rendering said bore impervious to gases, and a ceramic base resistance element in the bore bonded to the insulator and to the seal and constituting a part of the electrode in series with said section and seal, the resistance of said element being suicient t'o substantially reduce asuman erosion of the electrode by spark discharge,v and a secondAv ceramic base seal havinggood electricalv yhaving good electrical conductance overlying'A one end' of said section and securing andvsealingsaidsection.l in the bore, said seal being bonded to the insulator and rendering said bore impervious to gases, and a ceramic base resistance element in the borebonded to the'insulator and tof the sealY andconstituting a part of the electrode in series with said section and seal, the resistance of said element being suiicient to substantially reduce erosion of the electrode by spark discharge, and a second ceramic base sealhaving good electrical conductance overlying and bonded to the other end of` the resistance elementY and to the insulator, and-sealing the resistance elementV therein, and a second electrode section secured in said bore in good conducting relation with the second seal.

10. A spark plug comprising a shell, an insulator in the shell having a bore therein and an electrode in the bore comprising a section having its end normally exposed in ythe combustion chamber, a conducting seal securing and sealing said section in the bore and a non-porous resistance element in the bore bonded to the insulator and to the seal under heat and pressure, the resistance of said element being on the order of at least 60 ohms so as to reduce erosionV of the electrodes. by the spark.

ll. A spark plug comprising a shell, an insulator in the shell having a bore therein andk an electrode in the bore comprising a section having its end normally exposed in the combustion chamber, a conducting seal securing and sealing saidzsection in the bore and a non-porous resistance element in the bore bonded to the insulator and tc the seall under heat and pressure, the resistance of said element being on the order of at least 60 ohms so as to reduce erosion of the electrodes by the spark, and a conducting seal in the bore beyond the resistance element and bonded thereto and to the seal.

12. A spark plug comprising a shell, an insulator in the shell having a bore therein andY an electrode in thebore comprising a section having its end normally exposed in the combustion chamber, a conducting seal securing and sealing said section in the bore and a non-porous resistance element in the-bore bonded to thev insulator and-to the seal under heat and pressure, the resistance of. said element being onthe order of at. least 60l ohms soas to reduce erosionof the electrodes by the spa-rk, a conducting seal inthe bore beyond the resistance element, a conductor in the bore beyond the last named seal, said seal being bonded to the resistance element, and tothe insulator and having asubstantially gas-tight union with the said conductor.

lf3. kA spark. plug comprising a shell, an insulator in the shell having a bore therein and an electrode in the bore comprising a section having its end normally exposed in the combustion chamber, a conducting ceramic seal securing andv sealing said section in the bore, and a non-porous resistance element in the bore bonded to the insulator and to the seal under heat and pressure,

said resistance element comprising a fused; mix-4 ture of glass and carbonaceous material, the resistance of said element being on the order of at least GOohms so astofreduce erosion of-` the electrodes by the spark. v

le. A spark plug comprising a shell, an insulator in the shell havingr a bore therein and an'- electrode inthe bore comprising a sectionhaving` its end normally exposed in the combustionr chamber, aconducting ceramic seal securing and sealing said section in the bore,.and anon-porous resistance elementy inthe bore bonded to the insulator and to the seal under heat and pressure, said resistance element comprising a fused. mixture of glass, boron carbide and tungstencarbide, the resistance'of saidelement being on the order of at lea-st. 60 ohms so as to reduce erosion ofthe electrodes by the spark.

15 A spark plug comprising a shell, an insulator in the shell having a bore therein, an electrode.

in the bore comprising a section having its endnormally exposed in the combustion chamber and having a core of metal ci good heat conductivity,

a conducting ceramic seal securing and. sealingk saidsection in the bore, and. a noneporous-resistance element in the bore comprising. a fused mixture of ceramic insulating material and resistance material bondedlto the insulator and to the seal under pressure, the resistance of-A said resistancematerial being onv the order of at least 60 ohms` so as to. substantially reduce erosion of. the eleotrodes by the spark..

16. A heterogeneous electrically conducting structure comprising a skeleton of continuous substantially non-conducting glass bond in which are embodied in sequence along its length finely divided.' copper, nely divided carbon and finely divided copper.

17. A spark plug comprising a shell, an insulator in the shell having a bore therein andan electrode in the bore comprising. a resistance element consisting of a non-porous vitried mixture of heatresistant glass and carbon black of coarse particle size bonded and. compacted in the bore under heat and pressure, the4 resistance of said element being. sufficient to substantially reduce. erosion of. the electrode by spark discharge.

18. The combination of a sleeve of` insulating material, a heat and pressure compacted resistance element Within and closing the passage through the sleeve and thermally bonded thereto, and sealsv having goodelectrical conductance,

.overlying the ends of the resistance element and thermally bondedthereto and to the sleeve and protecting the element from the atmosphere, said element and seal having aceramic base, themelting point of said resistanceielement and said sealv @being substantially below the melting point of said sleeve to permit bonding of said element and seal thereto Without deforming said sleeve.

19. The combination of a sleeve of ceramic insulating material, a.y resistance: element Within and closingy the passage through the sleeve andy having a ceramic base, said element being sintered and thermally bonded to the sleeve, and a seal having a ceramic base and having good electricalconductance overlying the resistance element and thermally bonded thereto andfto thefsleeve and protecting the element from theV 20. The combination of a sleeve'ofceramic in'-` sulating. material, a sintered resistance element within and closing the passage through the. sleeve-1l andv having 4a ceramic base, said element being' thermally bonded to the sleeve, and seals having a ceramic base and good electrical conductance overlying the ends of the resistance element and thermally bonded thereto and to the sleeve and protecting the element from the atmosphere, the ceramic base of said resistance element and said seals being of glass having a melting point substantially below the melting point of said sleeve to permit bonding of said element and seal thereto without deforming said sleeve.

21. A resistance element consisting of a dense, vitried homogeneous mixture consisting of from 7.8 to 9% magnesium borate glass; from 11 to 25.6% fluorspar; from 1 to 4.6% carbon black; from 0 to 15% Whiting; from 0 to 15% beryl, and the balance borosilicate glass.

22. A resistance element comprising a skeleton of continuous substantially non-conducting glass bond in which are distributed in sequence along its length nely divided good conducting metal, nely divided carbon and nely divided good conducting metal.

TAINE G. McDOUGAL. KARL SCHWARTZWALDER. ALEXANDER S. RULKA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,764,311 Hunt June 17, 1930 1,806,347 Haverstick May 19, 1931 1,922,221 Steenbeck et al Aug. 15, 1933 1,960,316 Rabezzana May 29, 1934 1,976,901 Steenweg Oct. 16, 1934 1,978,323 Power Oct. 23, 1934 2,134,752 Ehlers Nov. 1, 1938 2,248,415 Schwartzwalder et al July 8, 1941 2,264,285 Bennett Dec. 2, 1941 2,280,962 McDougal Apr. 28, 1942 2,296,045 McDougal et al Sept. 15, 1942 2,305,577 Stoelting Dec. 15, 1942 FOREIGN PATENTS Number Country Date 363,615 Great Britain Dec. 14, 1931 

